1. Field of the Invention
This disclosure relates to optical inspection methods and apparatus, and in particular, to a method of optimizing a focus of an optical inspection apparatus having enhanced efficiency of detecting detects and a method and an apparatus of detecting defects using the focus optimizing method.
2. Description of the Related Art
Semiconductor devices are manufactured via various manufacturing processes, for example, using processes such as doping, diffusion, thermal oxidation, chemical vapor deposition, etching, exposure, etc. The above-mentioned processes are performed in sequence on a wafer or glass by process apparatuses.
When a manufacturing process is performed, the wafer or glass is examined for generated defects. As the wafer becomes larger, the time required for the examining process increases. Thus, manufacturing costs increase as well.
In order to examine defects of the wafer, a scanning electron microscope (SEM) is widely used. In a method of detecting defects by using the SEM, an electron beam is scanned on a wafer, and secondary electrons from the wafer are detected, so that the second electrons are converted into an image signal for detecting defects.
However, this method of detecting defects by using the SEM requires much time and cost. Furthermore, automation of the method is not possible.
Additionally, various methods of detecting defects or monitoring the manufacturing process have been disclosed. For example, Japan laid open publication number 1994-281409 discloses a method and apparatus of detecting defects. That is, when detecting defects of a wafer having multiple layers, each layer is focused independently to detect defects of the layer.
U.S. Pat. No. 6,338,926 discloses a method for easily finding an optimized focus. According to the method, a specially designed pattern is used for focusing. Korean laid open publication number 1999-72263 discloses a monitoring method and a monitoring apparatus. According to the method and the apparatus, a resolving power and focusing of the apparatus are monitored during the manufacturing processes, so that the focus data points are optimized.
Korean laid open publication number 1999-23205 discloses a conditional monitoring method of lithography and etching process, which provides an evaluating method for focus exposure and etching parameters.
However, none of the methods or apparatus described above teach or disclose a method of detecting defects by a relation between the focus and the defect detecting efficiency of an optical inspection apparatus. For example, when using an SEM electron beam, although many researches have been performed, however, in case of an optical inspection apparatus, no research about focusing, which is one of the factors related to defect detecting efficiency, has yet been systematically performed.
Thus, for conventional optical inspection apparatus, even for different layered films, the same focus is used, or an operator adjusts the focus according to his own experience. Consequently, the defect detecting efficiency is lowered, the time required to detect defects is greater, and the overall reliability and productivity of a semiconductor device decreases.